I have a used 2005 F150 supercrew flareside XLT 5.4
How do I indentify rear the axle ratio

 

First see this thread
Then see this one or this one or this one or this one.

 

Divide the tooth count on the ring gear by the tooth count on pinion gear.

 

Lol. Yeah you actually have to pull the whole carrier assembly out of the rearend and count the teeth. Sorry, no other way to do it.

 

On some axles, you can pull either the fill plug or the ABS sensor (the one on top of the diff) and turn the pinion until the numbers come around. The tooth count &/or ratio is stamped into the edge of the ring gear.

 

of course there is. the easiest way to check gear ratio in the axle is this:
jack up one rear tire off the ground. put the tranny in neutral. make a mark on the drive shaft. spin the tire that is off the ground ONE FULL ROTATION. as your are spinning it, count the number of times the mark on the driveshaft goes around. if the DS spins about three and a half times around, you have 3.55 gears. if the mark on the DS spins just over four times, you have 4.10, three and three forth turns, 3.73 gears, etc, etc.

 

There was supposed to be a hint of sarcasm in what I said. Read my first reply.

And IMO the easiest way would be to get the axle code off the door sticker and then come on here and look it up. But that's just me.

 

It's just a shame that when people swap out gears they don't bother to change the info on the door sticker. As long as it's 100% bone stock and never been touched, the door sticker works good. The other problem is a wrecked rebuild with a junkyard door, hence wrong sticker.

Don't they stick a tag under one of the bolts for the rear end cover like the old school rears that has the info on it?

 

My guess is it's probably illegal to alter that sticker. Perhaps you can go to the DMV and get a new one. And yes there is a tag on the rearend with some info on it. IMO when you buy a new gearset it should come with a new tag for the rearend.

 

The sticker is on the door jamb, not the door. If you suspect the rear has been changed and the axle tag itself is missing or suspected wrong, the easiest way is jack it up and do the count. I would jack up BOTH wheels and have 2 friends help you - spin BOTH rear wheels the same amount and watch the driveshaft.

 

Another thing is that if it is 4wd, it is highly unlikely that the sticker would be wrong. Most people are not dumb enough to put a new rearend on their truck without making sure that the gear ratio on the front and back are the same. For instance, I bought my truck used and blew the rearend a few months later. I knew that I had an open rearend, and when I rebuilt it that verified that it was an open diff. I replaced it with a limited slip. A bit later I looked up my axle code and it said I had a limited slip to begin with. So at some point somebody swapped the LS rearend with an open, for who knows what reason, but the gear ratio was the same.

Of course this all goes out the door if it's a 2wd.